1. Field of the Invention
The present invention is an improved construction of a plastic part used in manually propelled lawnmowers.
2. Description of the Related Art
Every effort is made to protect the operator of a manual pushed walk around grass cutter by constantly scrutinizing the device for opportunities to improve on the safety factor.
One area in need of improvement involves grass cutters that can be used with or without grass bag attachments. These grass cutters usually have a spring-loaded door permanently attached as part of the cutter body itself. When the cutter is used without a grass bag attached, the door is spring loaded closed, however, when a grass bag is used, its installation process requires that the spring-loaded door be hand held open. The entire bag and assembly is attached to the mower and the spring-loaded door is released. The door then rests on the surface of the plastic trim that surrounds the entire opening of the grass bag itself. The problem is that air escaping between the plastic trim on the bag, and the door surface (referred as blow back) is sufficient enough to cause concern for the operator""s safety.
Suggestions and attempts to reconfigure the plastic trim that contacts the door surface have been made, including the introduction of a small hollow ball as part of the plastic profile. The problem with this structure is in the selection of the plastic material used in this configuration. The pressure from the spring-loaded door compresses part of the ball because a good intimate contact must exist between the spring-loaded door and the material of choice for the hollow ball. The problem is that after hours of use, as the grass cutter tends to heat up, the hollow ball takes a permanent set, so that when the grass bag is removed, the ball becomes permanently distorted from the pressure from the spring loaded door and the elevated temperature.
The selection of the second plastic material for the hollow ball has many obstacles to overcome:
1. The adhesion between the two materials has to be intense enough to prevent separation between the two materials.
2. The hollow ball should be flexible enough to compress on contact with the door.
3. The heat distortion temperature must be equal to or better than the polyethylene presently used in the profile itself.
The present invention forms the ball from a second plastic material that is more flexible than the polyethylene material used in the prior art. The process for forming it is commonly referred to as co-extrusion. Two different plastics are extruded into one shape. When applied to the lawnmower structure, the adhesion between the basic profile and the co-extruded ball, must be extremely tight since any breakage or separation of the ball from the remainder of the structure will create a severe safety problem.
I have found a plastic material which, when compressed under load and heat, recovers its original shape, similar to a soft rubber product and still has the capability of adhering to the basic polyethylene profile, so as not to separate after continuous or repeated use and still return to its original shape.
A plastic material manufactured by Advanced Elastomer Systems, Akron, Ohio solved all of the above named problems. These products are commonly referred to as TPE (Thermoplastic Elastomer). Through the co-extrusion process, I have extruded a hollow ball of one material (TPE) onto a supporting clip of a second material (low density polyethylene). The final product has been tested and has solved the blow back problem.
The foregoing, as well as further objects and advantages of the invention will become apparent to those skilled in the art from a review of the following detailed description of my invention, reference being made to the accompanying drawings.